In case that a medicament is soluble in water or a solvent which is possible to be administered with the medicament, the medicament can be dissolved in the appropriate solvent to prepare a solution thereof and administered in the desired site or through an appropriate path way to deliver the medicament to the site. On the contrary, in case that a medicament is poorly soluble in water or other appropriate solvent which is possible to be administered with the medicament, the solubility of the medicament for water or the appropriate solvent can be enhanced by, for example, milling the medicament to a fine particle state or making the crystalline state of the medicament a high energy state, and then a suspension or the other may be prepared with the resulting soluble medicament to be used for administration.
In order that the efficacy of a medicament is effectively exerted, it is necessary that the medicament is exposed to the desired site at the desired concentration for the desired period. However, it is thought that the retentivity of said conventional solution or suspension is low at the desired site and hence it is difficult to keep the desired period and concentration at the site. Then, in order to enhance the local retentivity of the medicament or make it sustained-released, a different drug formulation such as gel formulation and ointment may be often used. Especially, ophthalmic formulations have been studied about a variety of drug formulations such as a gel formulation and an ointment formulation so that the medicament would not easily flow through wink or lacrimal fluid (JP-A-2003-95924, JP-A-6-116137 (1994), JP-A-2005-206598, JP-A-2001-518510, JP-B-6-67853 (1994), JP-2729859).
The gelation technique known currently includes a method gelatinizing an aqueous pharmaceutical composition comprising Pluronic with heating, a method gelatinizing an aqueous pharmaceutical composition comprising carboxyvinyl polymer through pH change, a method gelatinizing an aqueous pharmaceutical composition comprising gellan gum or alginic acid by adding an ionic material, etc.
In order to prepare a gel formulation of a fine particle, it seems easy to prepare a suspension comprising the fine particle at first and add a gelatinizing agent thereto and then make it gelatinized. However, if a gelatinizing agent is added to a suspension of a fine particle, the energy balance at the surface of the fine particle will be lost to lead the energy to lower state, i.e. the energy is supposed to change to agglutinate the fine particle (i.e. to decrease the superficial area thereof). In addition, the fine particle can also be agglutinated by heating, changing pH, changing ionic concentration or adding a salt. If the fine particle is agglutinated, the improved solubility will be lowered. Thus, a conventional gelatinizing agent such as Pluronic with heating or an anionic gelatinizing agent such as carboxyvinyl polymer and gellan gum might have a problem about the fine particle-aggregation when used.
The transparency of a suspension wherein the particle size of the fine particle is not more than 100 nm will be enhanced, however, if a gelatinizing agent is added to the suspension and then the fine particle is agglutinated, the suspension might be turned to white. A gel formulation for ophthalmic use is useful because it makes the retentivity in the anterior eye segment improved. However, when the gel formulation is turned to white, the use thereof will be restricted because of a long-term blurred vision caused by the white turbidity. Anyhow, it was difficult to prepare a gel formulation which exhibits high transparency and stability, by easily gelatinizing a suspension of a fine particle by adding a gelatinizing agent thereto.